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The Slack editor supports two modes: a Text editor for simple messages, and a JSONNET editor for rich Block Kit layouts with buttons, images, and structured sections.
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To send Slack notifications, you need a Slack vendor integrated with SuprSend. See Slack vendor integration for setup.

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Slack fields

Text mode — a single text field. Supports Handlebars variables ({{variable_name}}). Use triple braces {{{url}}} for URLs with special characters. JSONNET mode — a code editor that outputs Slack Block Kit JSON. Variables use data.key syntax (not Handlebars). Design visually in the Block Kit Builder first, then adapt the JSON into JSONNET. See the full JSONNET reference for syntax, examples, and debugging.
AI prompt — convert text to Block Kit: “Convert this Slack notification into Block Kit JSON: [paste message]. Variables: [list]. Return valid JSON I can adapt into JSONNET for SuprSend (replacing values with data.key).”
AI prompt — debug JSONNET: “Fix this JSONNET error from the SuprSend Slack editor. Error: [paste error]. Code: [paste JSONNET]. Variables are accessed as data.key or data[‘$special_key’].”
You can switch between Text and JSONNET at any time. Content is saved independently for each mode.

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Adding dynamic content

In Text mode — type {{ for auto-suggestions. Standard Handlebars syntax:
  • {{order_id}} — top-level variable
  • {{order.address.city}} — nested variable
  • {{{tracking_url}}} — URL (avoid escaping)
  • {{$recipient.name}} — recipient property
  • {{$brand.brand_name}} — tenant property
In JSONNET mode — variables use data.key syntax. See JSONNET variable reference for the full table. For conditionals, loops, and helpers in Text mode, see Handlebars Helpers.
If a variable cannot be rendered at send time (missing or mismatched data), SuprSend discards the Slack notification for that user. Other channels in the same template group are still sent.

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Preview and test

Text mode — the right panel shows a Slack message preview. It does not update automatically — refresh the page to see the latest changes. JSONNET mode — preview is not available in the editor. Click View on Slack Builder to render and validate your Block Kit output in Slack’s Block Kit Builder. Click Test in the top-right corner to send a real Slack message. This uses the live version — commit your changes before testing. See Testing a Template for the full guide.

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Commit

Click Commit in the top bar to publish the current draft as a new live version. Add an optional description for versioning.

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Common patterns

Slack automatically threads messages sent to the same channel with the same thread_ts. Pass a consistent thread_ts in your trigger payload to keep related messages threaded.
Use <@SLACK_USER_ID> to @mention a user. Pass the ID as a variable: <@{{assignee_slack_id}}>.
Slack uses <URL|display text> syntax. In JSONNET: "*<" + data.url + "|" + data.title + ">*".
Use :emoji_name: syntax (e.g., :white_check_mark:, :warning:).

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Frequently asked questions

Start with Text for simple alerts and status updates. Switch to JSONNET when you need buttons, images, structured layouts, or batched event lists.
Click View on Slack Builder in the JSONNET editor. Slack silently drops invalid blocks instead of showing errors — always validate before committing.
Slack truncates messages over 4000 characters. For batched notifications with many items, show the top 5-10 and add a “View all” button.
Slack uses mrkdwn, not standard Markdown. Bold: *text*, italic: _text_, strikethrough: ~text~, code: triple backticks.
SuprSend discards the Slack notification for that user. Other channels in the same template group are still sent.